1. Field of the Invention
The present invention relates to an apparatus for lighting LEDs (Light Emitting Diodes) used as, for example, a backlight for a liquid crystal display.
2. Description of the Related Art
An example of an apparatus for lighting LEDs is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-332624. This related art lights groups of series-connected LEDs with a voltage that is set to be always lower than a power source voltage irrespective of the number of the groups of series-connected LEDs, thereby enabling the use of low-withstand-voltage ICs and reducing a power loss.
FIG. 1 illustrates the apparatus according to the above-mentioned related art. The apparatus includes drivers 12 to 14 that turn on/off in response to time division signals S1 to S3. First ends of the drivers 12 to 14 are connected to terminals P23 to P25 that are connected to LEDs 21 to 26. The drivers 12 to 14 are connected in parallel with bypass units 15 to 17 that pass currents when the drivers 12 to 14 are OFF, the currents passed through the bypass units 15 to 17 being of such levels not to light the LEDs 21 to 26. A selector 18 selects one of drain-source voltages of the drivers 12 to 14, or one of currents passed through lines of the LEDs 21 to 26.
In a period to light the LEDs 21 to 26, the drivers 12 to 14 pass necessary currents to the LEDs 21 to 26, and in a period to turn off the LEDs 21 to 26, the drivers 12 to 14 stop the currents and the bypass units 15 to 17 pass minute currents to prevent an output voltage from a converter 27 from jumping.